Routing of data

Which of the following must be determined first by the router in order to route the data?

A. the distance metric of the data

B. the source address of the data

C. which routing protocol is used by the data

D. whether the protocol suite of the data is active

I may be splitting hairs, but an IPX packet never enters the router if IPX isn't already configured on an interface. If the protocol suite of the data (Appletalk, IPX, etc.) isn't active, the packet will never encounter the routing process. If the packet is dropped at the interface, does the router really make any decisions about how to route it?

Robert

How will it determine the metric if it doesnt know the routing protocol?

You could be us> A.

I would say D.

When the frame arrives, the ethertype field within the 802.2 SNAP header tells the router which protocol suite is the packet for. For instance ethertype 0x0800 is for IPv4, 0x8137 for IPX, 0x86DD for IPv6 and so on. IP routing is enabled by default on a router. But, if the packet is for the IP suite and IP has been disable with the "no ip routing" command, the packet is dropped. So the router has first to determine whether the protocol suite of the data is active. Another good reason to check this first is that many protocol suite can be active at the same time: IPv4, IPv6, DECnet, IPX, AppleTalk ....

Therefore, the router logic would be:

Determine the protocol suite reading the ethertype from the 802.2 SNAP If the protocol suite is a routed protocol then If the routed protocol is active then passes the packet to that routed protocol else drop the packet endIf else "This is not a routed protocol. Can be ARP, RARP, SNMP ..." endIf

Bernard.